A Pmk1-Regulated Mst12-Bip1 Network Coordinates Appressorium Function, Effector Deployment, and Invasive Growth by Magnaporthe oryzae

Abstract

To cause rice blast disease, the filamentous fungus Magnaporthe oryzae develops a specialised infection cell called an appressorium, which generates enormous turgor to breach the rice leaf cuticle. Although key regulators of appressorium development have been identified, it is not known how they drive the extensive transcriptional reprogramming required for infection-related morphogenesis. Here, we show that the Pmk1 MAP kinase orchestrates plant infection by regulating a transcriptional network controlled by the Mst12 and Bip1 transcription factors. Bip1 is regulated both by Pmk1-dependent phosphorylation and at the transcriptional level, while Mst12 binds to a cis-acting element upstream of BIP1 essential for pathogenesis. Bip1 and Mst12 are both necessary for regulating a set of Pmk1-dependent appressorium-specific genes, including transcriptional regulators, cell wall-degrading enzymes, and effector proteins. In addition, Mst12 specifically regulates functions required for appressorium-mediated penetration, while Bip1 controls a distinct sub-set of effector genes deployed during invasion of plant tissue. When considered together, these findings define a Pmk1-dependent transcriptional network required for plant infection by the blast fungus.